In the manufacture of many types of electrical assemblies, there is a need to apply solder at a particular site to either de-solder a device positioned at the site or solder a device placed at the site. One particular problem area resides in the manufacture of complex circuit boards where vast arrays of integraged circuits, resistors, capacitors and other types of semi-conductive devices are solder connected to circuit pads or terminals formed on the board and it becomes necessary to replace a a defectively connected device without damaging or disturbing adjacent devices. In such removal procedures, precaution must be taken to preclude damage to the circuit board and any plated through holes formed in the board.
At present the usual procedure contemplates use of a hand soldering iron in conjunction with a vacuum solder removal device which are used to melt and remove the solder to permit withdrawal of the defective device and the replacement with a new device. In some instances the board or a large number of components mounted on the board are defective, necessitating a junking of the board. Prior to such junking, good economics requires some procedure to remove the non-defective components from the board.
There are soldering devices available to apply molten solder to a particular site on a circuit board. One such device is marketed by Air-Vac Engineering Co., Inc., Milford, Conn., in which solder is forced from a well to apply a solder fountain against a selected site on a circuit board. In this device a piston moves through a chamber to force solder up through the well to form the fountain which overflows and is collected in a chamber surrounding the cylinder. The piston is driven by a rod acting through close-fitting bearings mounted in the bottoms of the cylinders and the chamber containing the solder. A port is formed in the cylinder wall and is valved by the piston to permit the flow of excess solder from the overflow chamber back into the cylinder.
In U.S. Pat. No. 1,272,358 there is disclosed a soldering device in which pressurized air is impinged on a contained solder pool so that solder is forced from the pool through a tube to a soldering site. Overflow solder is collected and returned through a valve to the pool.
As the printed circuit board art has developed, numerous types of wave soldering devices have been developed to mass solder large numbers of components having leads extending through the boards to circuit paths and pads formed on the board. Again, these devices depend for operation upon the use of various types of pumps which have closely fitted parts exposed to contaminants, such as fluxes, in the molten solder.
In these prior art devices, pumps and valves of one sort or another are utilized wherein the moving parts are closely fitted to move along or into bearing or seating surfaces. Experience has demonstrated that these devices need frequent servicing because of inclusions from the solder being deposited between the tight-fitting moving or engaging surfaces.